The present invention relates to a method of manufacturing a semiconductor integrated circuit device, and more particularly to a method of manufacturing a semiconductor device used as an image sensing device having a charge coupled device (CCD) and its peripheral circuits on the same substrate.
Recently, a CCD, a driver for driving the CCD, a logical circuit for processing signal and the like are fabricated on the same semiconductor substrate as an integrated one-chip device. The fabrication of the CCD and its peripheral circuit on the same substrate has many advantages in system construction, such as omission of external clock lines, and an improved operation speed of the entire system.
An example of such devices is disclosed, e.g., in a paper of a title "CCD Delay Line with Integrated CMOS Driver" by Sakagami et al., presented at the Joint Meeting of Four Electric Societies in Japan, 1977, pp. 4-28 to 4-31.
A semiconductor device having a CCD and its peripheral transistor circuit fabricated on the same substrate, however, is necessarily associated with the problem of a low threshold level of transistors in the peripheral circuit, thus resulting in a small logical amplitude margin of CMOS transistors and a liability to defective operation.